1. Field of Invention
A retention assembly for a hydrocarbon trap is incorporated into an air induction system of a motor vehicle having a combustion engine in order to secure the trap and reduce hydrocarbon emissions.
2. Description of Related Art
Under the increasingly stringent California LEV (Low Emission Vehicle) II standards and United States Environmental Protection Agency (EPA) Tier II standards, automakers are required to dramatically reduce the amount of evaporative emissions from their gasoline-powered vehicles (by 75% for California's LEV II program and by 52.5% for the EPA's Tier 2 program). By 2007, all gasoline-powered vehicles will be required to meet these standards for evaporative emissions.
Evaporative emissions are hydrocarbon (HC) vapors that come from sources in a motor vehicle other than the exhaust system. Major sources of evaporative emissions include a motor vehicle's air intake system, fuel rail, exhaust gas recirculation system, and gas tank.
Hydrocarbon traps can be used to adsorb hydrocarbon vapors and reduce hydrocarbon emissions. Hydrocarbon traps typically comprise adsorbent media such as zeolites or activated carbon. The adsorbent media can be contained within, or supported by, a porous carrier or substrate. Useful hydrocarbon traps are commercially available, e.g., from Engelhard Corporation (Iselin, N.J.).
Hydrocarbon traps can be placed in the air induction system between a vehicle's air cleaner and engine where they can capture hydrocarbons that are escaping through the air intake when the engine is stopped. The incorporation of a hydrocarbon trap in this location is desirable because the air intake system is estimated to contribute as much as 50% of total evaporative emissions.
In use, the trap adsorbs hydrocarbons that are emitted when the engine is stopped. Once the vehicle is started and driven, the trap releases the hydrocarbons into the engine where they are burned. By trapping and later burning the hydrocarbon vapors, hydrocarbon emissions from the vehicle can be reduced.
Preferred hydrocarbon traps are designed to be tamper proof and free of on-board diagnostic (OBD) equipment. Hydrocarbon traps preferably remain effective for the life of the vehicle, have minimal impact on airflow into the engine, and can withstand exposure to ice, water, salt, dust, air filter surfactants and engine backfire.
As noted above, hydrocarbon traps typically comprise adsorbent media supported by a porous carrier or substrate. The substrate is inserted into an air tube such as the outlet duct of a vehicle's air cleaner. Preferably, the substrate is adapted to fit snugly within the outlet duct so as to prevent vibration of the substrate. Vibration may lead to undesired noise or even damage to the trap. Furthermore, a snug fit within the outlet duct causes a majority of the gases passing through the outlet duct to pass through (rather than around) the hydrocarbon trap, thus maximizing its efficiency. Gases passing through the hydrocarbon trap are directed via the clean air duct to the engine. To connect the air cleaner to the clean air duct, an inlet of the clean air duct is connected to the air cleaner outlet duct.
Thermal stresses acting upon an unsecured hydrocarbon trap can produce undesired results. The air cleaner outlet duct, which typically is made of synthetic resin material, and the trap substrate, which may, for example, be made of metal, are subject to changes in temperature due to, for example, environmental and engine-operating conditions. As a result of the respective thermal expansion coefficients of the trap substrate and the synthetic resin outlet duct under conditions of increasing temperature, the outlet duct resin will typically expand more than the trap substrate. Because the dimensions of the synthetic resin outlet duct will increase more than the dimensions of the trap substrate, the snug fit between the outlet duct and the substrate will be compromised, which may result in undesired noise, adsorptive inefficiency and possibly permanent damage to the trap.
Accordingly, it would be an advantage to provide a retention assembly capable of securing a hydrocarbon trap within a vehicle's air induction system, and specifically within an air cleaner outlet duct, in order to minimize the effects of thermal expansion coefficient mismatch and maximize the abatement of hydrocarbon emissions.